Since you're going around saying "I don't get it". The thing here is that it's a drop down menu, I guess. If white was the menu default, then that's what white people would use, but yellow in an emoticon context is already coded as white (despite the broader cultural context where it's East Asian), so going out of your way to pick a more explicitly white tone is weird. You say that the purpose is for "expression" and then deny that it expresses anything. My question is why would someone feel the need to express more explicitly that they are white?

This doesn't matter, but if you showed me a lengthy text message and asked me about a specific use of "can't" over "cannot", I could probably give you an assessment of something like that as well if you really wanted one. No one here thinks this is an important issue, but they are attempting to articulate an opinion in response to the particular claim made.